U.S. patent application number 12/577698 was filed with the patent office on 2010-12-30 for enhanced battery storage and recovery energy systems.
This patent application is currently assigned to TIGO ENERGY, INC.. Invention is credited to Mordechay AVRUTSKY, Dan KIKINIS.
Application Number | 20100327807 12/577698 |
Document ID | / |
Family ID | 43379935 |
Filed Date | 2010-12-30 |
![](/patent/app/20100327807/US20100327807A1-20101230-D00000.png)
![](/patent/app/20100327807/US20100327807A1-20101230-D00001.png)
![](/patent/app/20100327807/US20100327807A1-20101230-D00002.png)
![](/patent/app/20100327807/US20100327807A1-20101230-D00003.png)
![](/patent/app/20100327807/US20100327807A1-20101230-D00004.png)
![](/patent/app/20100327807/US20100327807A1-20101230-D00005.png)
![](/patent/app/20100327807/US20100327807A1-20101230-D00006.png)
![](/patent/app/20100327807/US20100327807A1-20101230-D00007.png)
![](/patent/app/20100327807/US20100327807A1-20101230-D00008.png)
United States Patent
Application |
20100327807 |
Kind Code |
A1 |
KIKINIS; Dan ; et
al. |
December 30, 2010 |
Enhanced Battery Storage and Recovery Energy Systems
Abstract
Systems and methods are herein disclosed for efficiently and
cost-effectively balancing the voltages across batteries and/or
cells in an energy storage system. A controller monitors the
battery voltages and instructs regulator circuits to balance
voltages between any batteries or sets of batteries having
imbalanced voltages. Regulator circuits implementing a modified uk
converter can be utilized. Regulator circuits can have two
capacitive circuits, one inductive circuit, and two switches. Two
capacitors, an inductor, and two field effect transistors can be
used in each regulator circuit.
Inventors: |
KIKINIS; Dan; (Saratoga,
CA) ; AVRUTSKY; Mordechay; (Alfei Menashe,
IL) |
Correspondence
Address: |
GREENBERG TRAURIG, LLP (SV);IP DOCKETING
2450 COLORADO AVENUE, SUITE 400E
SANTA MONICA
CA
90404
US
|
Assignee: |
TIGO ENERGY, INC.
Los Gatos
CA
|
Family ID: |
43379935 |
Appl. No.: |
12/577698 |
Filed: |
October 12, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61269652 |
Jun 25, 2009 |
|
|
|
Current U.S.
Class: |
320/116 |
Current CPC
Class: |
Y02T 10/70 20130101;
Y02T 10/7055 20130101; H02J 7/0016 20130101 |
Class at
Publication: |
320/116 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Claims
1. An energy storage system comprising: two or more batteries
connected in series and forming two sets of batteries; a regulator
circuit configured to balance voltages across the two sets of
batteries, the regulator circuit comprising at least one switchable
connection and at least one energy storage unit, wherein the at
least one switchable connection connects the at least one energy
storage unit to the two sets of batteries; and a controller
connected to the regulator circuit and configured to: monitor
voltages across the two sets of batteries; identify voltage
imbalances between the two sets of batteries; and adjust the
regulator circuit so that the voltage imbalances between the two
sets of batteries are minimized.
2. The energy storage system of claim 1, wherein the at least one
switchable connection comprises one or more transistors.
3. The energy storage system of claim 1, wherein the at least one
energy storage unit comprises one or more inductive circuits.
4. The energy storage system of claim 1, wherein the at least one
energy storage unit comprises one or more capacitive circuits.
5. The energy storage system of claim 1, wherein the regulator
circuit comprises: two capacitive circuits each connected in
parallel with one of the two sets of batteries; an inductive
circuit connected to: the two capacitive circuits; and the two sets
of batteries; two switches each connected to: the inductive
circuit; one of the two capacitive circuits; one of the two sets of
batteries; and the controller.
6. The energy storage system of claim 5, wherein the two switches
operate at a fifty percent duty cycle when the voltages across the
two sets of batteries are equal.
7. The energy storage system of claim 5, wherein the two switches
operate at a duty cycle not equal to fifty percent when the
voltages across the two sets of batteries are not equal, and
wherein the duty cycle is such that the voltages across the two
sets of batteries converge.
8. The energy storage system of claim 5, wherein the two switches
are transistors.
9. The energy storage system of claim 1, comprising: 2.sup.n number
of batteries, where n is any positive integer; and 2.sup.n/2 number
of regulator circuits.
10. The energy storage system of claim 1, wherein the regulator
circuit is turned off when the voltages across the two sets of
batteries are balanced.
11. The energy storage system of claim 1, wherein the controller is
further configured to: monitor the direction of current through the
batteries; and determine whether the batteries are being charged or
discharged.
12. A method comprising: monitoring a first voltage across a first
set of batteries; monitoring a second voltage across a second set
of batteries; determining if a difference between the first voltage
and the second voltage exceeds a voltage imbalance threshold; and
instructing a regulator circuit, associated with the first set of
batteries and the second set of batteries, to balance the first
voltage and the second voltage by: storing bypass energy in an
energy storage unit; and distributing the stored bypass energy to
at least one of the first set of batteries and the second set of
batteries.
13. The method of claim 12, wherein the instructing further
comprises adjusting a duty cycle of two switches in the regulator
circuit.
14. An energy storage system comprising: a first set of batteries
having a first voltage; a second set of batteries having a second
voltage, wherein the first and second sets of batteries are
connected in series; a regulator circuit configured to balance the
first voltage and the second voltage, and wherein the regulator
circuit comprises: an inductive circuit; a first switch; and a
second switch; and a controller connected to the regulator circuit
and configured to: monitor the first voltage and the second
voltage; identify a voltage imbalance between the first voltage and
the second voltage; and adjust the first switch and the second
switch to minimize the voltage imbalance between the first voltage
and the second voltage.
15. The energy storage system as recited in claim 14, wherein the
regulator circuit further comprises: a first capacitive circuit;
and a second capacitive circuit.
16. The energy storage system as recited in claim 15, wherein: the
first capacitive circuit is connected to: the first set of
batteries; and the second set of batteries; the second capacitive
circuit is connected to: the first set of batteries; the second set
of batteries; and the first capacitive circuit; the inductive
circuit is connected to: the first set of batteries; the second set
of batteries; the first capacitive circuit; and the second
capacitive circuit; the first switch is connected to: the first set
of batteries; the first capacitive circuit; the inductive circuit;
the second switch; and the controller; and the second switch is
connected to: the second set of batteries; the second capacitive
circuit; the inductive circuit; the first switch; and the
controller.
17. The energy storage system as recited in claim 15, wherein: the
first capacitive circuit is in parallel with the first set of
batteries; and the second capacitive circuit is in parallel with
the second set of batteries.
18. The energy storage system as recited in claim 15, wherein the
inductive circuit comprises a second terminal connected to: a
second terminal of the first capacitive circuit; and a first
terminal of the second capacitive circuit.
19. The energy storage system as recited in claim 14, wherein the
controller is configured to: identify a voltage imbalance when a
difference between the first voltage and the second voltage exceeds
a voltage imbalance threshold; and adjust a duty cycle of the first
switch and the second switch, so that the difference between the
first voltage and the second voltage, decreases.
20. The energy storage system as recited in claim 14, wherein the
controller is connected to: the first set of batteries; and the
second set of batteries.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of Provisional
U.S. Patent Application Ser. No. 61/269,652, filed Jun. 25, 2009
and entitled "Enhanced Battery Storage and Recovery Energy
Systems," the disclosure of which is hereby incorporated by
reference.
FIELD OF THE TECHNOLOGY
[0002] At least some embodiments of the disclosure relate to energy
storage systems in general, and more particularly but not limited
to, enhancing the efficiency and number of batteries in a
rechargeable energy storage system.
BACKGROUND
[0003] Rechargeable energy storage systems having a large number of
batteries that can charge and discharge with great efficiency may
become increasingly important in the coming years. For instance
electric and hybrid cars may benefit from larger energy storage
systems and efficient charging and discharging. To supplement wind
and solar power generation when there are lulls in the wind or
diminished sunlight, large and efficient energy storage systems
will be needed in homes and as part of the power grid. Even today's
rechargeable laptop computers and cell phones can benefit from more
efficient charging and recharging. All of these energy storage
systems can operate more effectively if the voltage between
batteries is balanced. Current systems for balancing voltages are
inefficient and these inefficiencies typically only get worse as
the number of batteries increases (larger energy storage
systems).
[0004] A battery is a combination of one or more electrochemical
cells connected in series. Each cell produces a voltage, and when
connected in series, a stack of cells (battery) produces a voltage
equal to the sum of the cells comprising the battery. Each battery
thus produces a voltage, and when connected in series, an energy
storage system (comprising one or more batteries connected in
series) produces a voltage equal to the sum of the batteries
comprising the energy storage system. Voltage imbalances between
batteries decrease system efficiency and limit the number of
batteries that can be connected in series. Importantly, voltage
imbalances may become harder to mitigate as the number of batteries
connected in series increases.
[0005] At the same time, the number and importance of applications
requiring large rechargeable energy storage systems are growing.
For instance, homes relying to a large extent or exclusively on
wind and/or solar power require large energy storage systems in
order to supplement the wind and/or solar power when there is low
wind speed or a lack of sunlight. The same problem threatens future
power grids since they too will rely largely on wind and solar
power. Thus, large energy storage systems are a key to enabling
renewable energy to power homes and power grids. Many other
applications will also benefit from or require large rechargeable
energy storage systems.
SUMMARY OF THE DESCRIPTION
[0006] Systems and methods in accordance with the present invention
are described herein. Some embodiments are summarized in this
section.
[0007] In one of many embodiments of the present invention,
apparatuses include an energy storage system. The energy storage
system comprises two or more batteries connected in series. The two
or more batteries form two sets of batteries wherein each set of
batteries can comprise one or more batteries. The energy storage
system comprises a regulator circuit configured to balance voltages
across the two sets of the batteries. The regulator circuit may
comprise at least one switchable connection and at least one energy
storage unit. The at least one switchable connection may connect
the at least one energy storage unit to the two sets of batteries.
The energy storage system comprises a controller connected to the
regulator circuit. The controller is configured to monitor voltages
across the two sets of the batteries. The controller is configured
to identify voltage imbalances between the two sets of the
batteries. The controller is configured to adjust the regulator
circuit so that the voltage imbalances between the two sets of the
batteries are minimized.
[0008] In another embodiment of the present invention, a method of
operating an energy storage system includes monitoring a first
voltage across a first set of batteries. The method also includes
monitoring a second voltage across a second set of batteries. The
method also includes determining if a difference between the first
voltage and the second voltage exceeds a voltage imbalance
threshold. The method also includes instructing a regulator
circuit, associated with the first set of batteries and the second
set of batteries, to balance the first voltage and the second
voltage. The regulator circuit accomplishes this balancing by
storing bypass energy in an energy storage unit. The stored bypass
energy is then distributed to one of the sets of batteries.
[0009] In another embodiment of the present invention, apparatuses
include an energy storage system. The energy storage system
comprises a first set of batteries having a first voltage. The
energy storage system comprises a second set of batteries having a
second voltage. The first and second sets of batteries are
connected in series. The energy storage system comprises a
regulator circuit. The regulator circuit is configured to balance
the first voltage and the second voltage. The regulator circuit
comprises an inductive circuit, a first switch, and a second
switch. The energy storage system includes a controller connected
to the regulator circuit. The controller is configured to monitor
the first voltage and the second voltage. The controller is
configured to identify a voltage imbalance between the first
voltage and the second voltage. The controller is configured to
adjust the first switch and the second switch to minimize the
voltage imbalance between the first voltage and the second
voltage.
[0010] Other embodiments and features of the present invention will
be apparent from the accompanying drawings and from the detailed
description which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The embodiments are illustrated by way of example and not
limitation in the figures of the accompanying drawings in which
like references indicate similar elements.
[0012] FIG. 1a illustrates an embodiment of an energy storage
system having a plurality of batteries, a plurality of regulator
circuits, and a controller.
[0013] FIG. 1b illustrates an embodiment of an energy storage
system having a plurality of batteries, a plurality of regulator
circuits, and a controller.
[0014] FIG. 2 illustrates an embodiment of a regulator circuit.
[0015] FIG. 3 illustrates an embodiment of an energy storage system
having four batteries and two regulator circuits.
[0016] FIG. 4 illustrates an embodiment of an energy storage system
having eight batteries and four regulator circuits.
[0017] FIG. 5 illustrates an embodiment of an energy storage system
having five batteries and four regulator circuits.
[0018] FIG. 6 illustrates a first embodiment of a method of
operating the herein disclosed energy storage system.
[0019] FIG. 7 illustrates a second embodiment of a method of
operating the herein disclosed energy storage system.
DETAILED DESCRIPTION
[0020] The following description and drawings are illustrative and
are not to be construed as limiting. Numerous specific details are
described to provide a thorough understanding. However, in certain
instances, well known or conventional details are not described in
order to avoid obscuring the description. References to one or an
embodiment in the present disclosure are not necessarily references
to the same embodiment; and, such references mean at least one.
[0021] The present disclosure describes an energy storage system
and methods for storing energy, wherein voltage variations between
batteries and/or cells are efficiently (for example, losses as low
as 1-3% approximately) minimized at relatively low cost. This may
be accomplished via using one or more regulator circuits to balance
voltages between sets of batteries. In an embodiment, the one or
more regulator circuits may comprise at least one energy storage
unit and at least one switchable connection. In an embodiment, the
one or more regulator circuits may be modified uk converters. In an
embodiment, the one or more regulator circuits may comprise at
least a low impedance inductor, at least two low impedance
capacitors, and at least a pair of cycling transistors to balance
voltages across sets of cells while converting only minimal energy
into heat (low losses).
[0022] FIG. 1a illustrates an embodiment of an energy storage
system having a plurality of batteries, a plurality of regulator
circuits, and a controller. For the purposes of this disclosure, a
battery is an energy storage device having one or more
electrochemical cells (or cells) configured to store energy. A
battery can have positive and negative terminals. The positive and
negative terminals of two batteries can be connected via a
conductive medium to form part of an energy storage system. Any
number of batteries can be connected in this fashion. As more
batteries are added to the energy storage system, the energy
storage system voltage output increases and is equal to the sum of
the voltages across each of the batteries. For instance, in FIG.
1a, the battery voltage V.sub.B is the sum of the first voltage and
the second voltage (V.sub.B=V.sub.1+V.sub.2).
[0023] Each battery comprises one or more cells. The number of
cells in a battery may be limited by voltage imbalances between
cells. In order to avoid the expense and complexity of balancing
cells, the number of cells in a battery may be limited to such a
number that cell voltage balancing is not necessary. The number of
cells that can be connected in series without the need for cell
voltage balancing varies from one battery type to another. For
instance, cell regulation is more important in Li and Li-Ion
batteries, where voltage imbalances may not just lead to
inefficiency but also to fire and explosion. For the purposes of
this disclosure, the number of cells in a battery may be assumed to
be the maximum number of cells for a given battery type that do not
require cell voltage balancing.
[0024] The energy storage system 100 comprises two or more
batteries 102, 104 connected in series to form a portion of the
energy storage system 100. The batteries are rechargeable and can
either be charged by a charger/load device 160, or can discharge
energy into a charger/load device 160. The charger/load device 160
can comprise one or more devices (e.g., multiple power sources or
multiple resistive loads). A first voltage V.sub.1 across the first
battery 102, and a second voltage V.sub.2 across the second battery
104 may be monitored. In an embodiment, a controller 150 monitors
V.sub.1 and V.sub.2. In the illustrated embodiment, the controller
150 monitors the first and second voltages V.sub.1, V.sub.2 via
connection to a regulator circuit 110. In another embodiment (not
illustrated), the controller can directly monitor the voltages
V.sub.1, V.sub.2 across the first and second batteries 102, 104.
For instance, the controller 150 may have connections to terminals
of the batteries 102, 104 whereby the voltages V.sub.1, V.sub.2
across the batteries 102, 104 can be measured.
[0025] If the first voltage V.sub.1 across the first battery 102
varies significantly from the second voltage V.sub.2 across the
second battery 104, then the regulator circuit 110 may balance or
minimize the voltages V.sub.1, V.sub.2 such that the voltages
V.sub.1, V.sub.2 are equal. In an embodiment, balancing the
voltages means adjusting the voltages V.sub.1, V.sub.2 such that
they are within a voltage imbalance threshold V.sub.T of each
other. For instance, if the voltage imbalance threshold is 0.2V,
balancing the voltages means that two voltages will be adjusted
until they are within 0.2V of each other. In an embodiment,
balancing the voltages means adjusting one of the two voltages
V.sub.1, V.sub.2 until it is within the voltage imbalance threshold
V.sub.T of the other voltage. For instance, if the voltage
imbalance threshold is 0.3V and the first voltage V.sub.1 is
100.0V, and the second voltage V.sub.2 is 99.3V, then balancing the
voltages may mean adjusting V.sub.2 until it is greater than 99.7V.
Alternatively, the larger voltage could be decreased until it is
within V.sub.T of the smaller voltage.
[0026] Given more than two batteries in series, more than one
regulator circuit 110 may be used. Furthermore, when more than two
batteries are used, the regulator circuits 110 may balance voltages
across sets of batteries rather than just across individual
batteries. For instance, given four batteries A, B, C, and D, a
regulator circuit may balance the voltages across the following two
sets of batteries: (1) A and B; and (2) C and D.
[0027] In an embodiment, the regulator circuit 110 may comprise one
or more energy storage units 112, 114 and one or more switchable
connections 122, 124. As indicated in FIG. 1a, the second energy
storage unit 114 and the second switchable connection 124, are
optional, as are any third, fourth, or fifth energy storage units
or switchable connections (not illustrated).
[0028] The switchable connection 122 may comprise one or more
switches. A switch may be a transistor. In an embodiment, the one
or more switchable connections 122, 124 are configured to allow
energy (voltage and/or current) to bypass the second battery 104.
The one or more switchable connections are further configured to
route the bypass energy to the one or more energy storage units
112, 114. For the purposes of this disclosure, "bypass energy" is
current and/or voltage that, rather than being provided to or
discharged from the first or second sets of batteries, is routed to
one or more energy storage units. From the energy storage units,
the stored bypass energy can be distributed to one of the sets of
batteries.
[0029] In an embodiment, an energy storage unit may comprise an
inductive circuit. In an embodiment, an inductive circuit may
comprise an inductor. Thus, bypass energy may be stored in an
inductive circuit (e.g., inductor). In an embodiment, the at least
one energy storage unit 112, 114 comprises at least one capacitive
circuit. The one or more capacitive circuits may be capacitors. The
capacitors may filter voltage and/or current spikes (e.g., ripple
currents). Capacitors may also store bypass energy.
[0030] The one or more switchable connections 122, 124 are further
configured to route bypass energy that is stored in the one or more
energy storage units 112, 114 to either the first or second battery
102, 104. In an embodiment, a switchable connection 122, 124 may be
a switch (e.g., transistor). In an embodiment, the first switchable
connection 122 can comprise two switches: one configured to store
bypass energy in the energy storage unit 112, and one configured to
distribute the stored bypass energy to either of the batteries 102,
104. Given an embodiment having two switches, one of the switches
may be a transistor and one of the switches may be a diode.
[0031] For the purposes of this disclosure, a "set of batteries"
means one or more batteries. In an embodiment, a set of batteries
can include a single battery. Thus, for example, when reference is
made to balancing two sets of batteries having a first voltage
V.sub.1 and a second voltage V.sub.2, respectively, where each set
of batteries comprises a single battery, what is meant is that the
voltages across the two individual batteries are being balanced
(e.g., V.sub.1=V.sub.2).
[0032] In an embodiment, a set of batteries can include two or more
batteries. Thus, for example, when reference is made to balancing
two sets of batteries, where each set of batteries comprises two
batteries, (assume a voltage across each of the four batteries as
follows: V.sub.1, V.sub.2, V.sub.3, and V.sub.4) what is meant is
that the voltage across one of the two pairs of batteries is being
balanced with the voltage across the other pair of batteries (e.g.,
V.sub.1+V.sub.2=V.sub.3+V.sub.4).
[0033] In an embodiment, a set of batteries can include one
battery, or two or more batteries. Thus, for example, when
reference is made to balancing two sets of batteries, where a first
set comprises one battery, A, and the second set comprises three
batteries, B, C, and D, what is meant is that the voltage across
battery A is being balanced relative to the average voltage across
batteries B, C, and D (e.g., V.sub.A=(V.sub.B+V.sub.C+V.sub.D)/3).
As a further example of this third embodiment, when reference is
made to balancing two sets of batteries, where a first set
comprises two batteries A and B, and the second set comprises three
batteries C, D, and E, what is meant is that the average voltage
across batteries A and B is being balanced relative to the average
voltage across batteries C, D, and E (e.g.,
(V.sub.A+V.sub.B)/2=(V.sub.c+V.sub.D+V.sub.E)/3). The details of
such balancing are discussed later in this disclosure.
[0034] In an embodiment, sets of batteries can overlap. For
instance, given three batteries, A, B, and C, a first set of
batteries may comprise batteries A and B. A second set of batteries
may comprise batteries B and C. Hence, the first and second sets of
batteries both comprise battery B. While some embodiments of the
energy storage system 100 will involve balancing the voltages of
individual batteries relative to other individual batteries, often
balancing will take place between sets of batteries.
[0035] For the purposes of this disclosure, a "terminal" is a point
on an electrical component where an electrical connection can be
made. Inductors, capacitors, resistors, transistors, and batteries
generally include at least a first and second terminal. Switches
and transistors may additionally have a gate terminal used to
control switching. With reference to the figures, the first
terminal is that which is closest to the top of a figure for
components that are shown as vertically-oriented, and closest to
the right of a figure for components that are shown as
horizontally-oriented.
[0036] For the purposes of this disclosure, a "voltage imbalance"
means the circumstance where two or more battery voltages are not
equal or differ by at least a voltage imbalance threshold V.sub.T.
Voltage imbalance may cause a battery to charge or discharge
inefficiently or worse can cause overcharging and potentially
explosion or fire. Voltage imbalance may depend on the type of
battery. For instance, many batteries, like Lead Acid, Nickel
Cadmium, and Nickel-Metal Hydride, have greater tolerance for
voltage imbalance than do Li or Li-Ion batteries. Moreover, the
risk of explosion or fire may be greater with Li-Ion batteries.
Thus, it may be desirable to seek less voltage imbalance in Li and
Li-Ion batteries than other battery types. Throughout this
disclosure reference will be made to balancing and minimizing
voltage imbalances and to convergence of voltages. These terms and
phrases are interchangeable. A voltage imbalance may also be
referred to as a variation in voltage.
[0037] For the purposes of this disclosure, "minimized" means any
convergence of two voltages. In an embodiment, minimizing voltage
imbalances means adjusting voltages such that they converge on an
average. For instance, the two voltages 50V and 100V may be
adjusted so that they converge to 75V. In another embodiment,
minimizing voltages means adjusting voltages such that they
converge on a voltage that is not an average. For instance, the two
voltages 50V and 100V may be adjusted so that they converge on
100V. As another example, the two voltages 50V and 100V may be
adjusted so that they converge on 90V.
[0038] One should further understand that the systems herein
disclosed can also be implemented to balance voltages between cells
or between cells as well as between batteries. For instance, see
FIG. 1b.
[0039] FIG. 1b illustrates an embodiment of an energy storage
system having a plurality of cells, a plurality of regulator
circuits, and a controller.
[0040] The energy storage system 100 comprises two or more cells
102, 104 connected in series to form a battery. The battery is
rechargeable and can either be charged by a charger/load device
160, or can discharge energy into a charger/load device 160. The
charger/load device 160 can comprise one or more devices (e.g.,
multiple power sources or multiple resistive loads). A first
voltage V.sub.1 across the first cell 102, and a second voltage
V.sub.2 across the second cell 104 may be monitored. In an
embodiment, a controller 150 monitors V.sub.1 and V.sub.2. In the
illustrated embodiment, the controller 150 monitors the first and
second voltages V.sub.1, V.sub.2 via connection to a regulator
circuit 110. In another embodiment (not illustrated), the
controller can directly monitor the voltages V.sub.1, V.sub.2
across the first and second cells 102, 104. For instance, the
controller 150 may have connections to terminals of the cells 102,
104 whereby the voltages V.sub.1, V.sub.2 across the cells 102, 104
can be measured.
[0041] If the first voltage V.sub.1 across the first cell 102
varies significantly from the second voltage V.sub.2 across the
second cell 104, then the regulator circuit 110 may balance or
minimize the voltages V.sub.1, V.sub.2 such that the voltages
V.sub.1, V.sub.2 are equal. In an embodiment, balancing the
voltages means adjusting the voltages V.sub.1, V.sub.2 such that
they are within a voltage imbalance threshold V.sub.T of each
other. For instance, if the voltage imbalance threshold is 0.2V,
balancing the voltages means that two voltages will be adjusted
until they are within 0.2V of each other. In an embodiment,
balancing the voltages means adjusting one of the two voltages
V.sub.1, V.sub.2 until it is within the voltage imbalance threshold
V.sub.T of the other voltage. For instance, if the voltage
imbalance threshold is 0.3V and the first voltage V.sub.1 is
100.0V, and the second voltage V.sub.2 is 99.3V, then balancing the
voltages may mean adjusting V.sub.2 until it is greater than 99.7V.
Alternatively, the larger voltage could be decreased until it is
within V.sub.T of the smaller voltage.
[0042] For batteries comprising more than two cells, more than one
regulator circuit 110 may be used. Furthermore, when more than two
cells are used, the regulator circuits 110 may balance voltages
across sets of cells rather than just across individual cells. For
instance, given four cells A, B, C, and D, a regulator circuit may
balance the voltages across the following two sets of cells: (1) A
and B; and (2) C and D.
[0043] For the purposes of this disclosure, a "set of cells" means
one or more cells. In an embodiment, a set of cells can include a
single cell. Thus, for example, when reference is made to balancing
two sets of cells having a first voltage V.sub.1 and a second
voltage V.sub.2, respectively, where each set of cells comprises a
single cell, what is meant is that the voltages across the two
individual cells are being balanced (e.g., V.sub.1=V.sub.2).
[0044] In an embodiment, a set of cells can include two or more
cells. Thus, for example, when reference is made to balancing two
sets of cells, where each set of cells comprises two cells, (assume
a voltage across each of the four cells as follows: V.sub.1,
V.sub.2, V.sub.3, and V.sub.4) what is meant is that the voltage
across one of the two pairs of cells is being balanced with the
voltage across the other pair of cells (e.g.,
V.sub.1+V.sub.2=V.sub.3+V.sub.4).
[0045] In an embodiment, a set of cells can include one cell, or
two or more cells. Thus, for example, when reference is made to
balancing two sets of cells, where a first set comprises one cell,
A, and the second set comprises three cells, B, C, and D, what is
meant is that the voltage across cell A is being balanced relative
to the average voltage across cells B, C, and D (e.g.,
V.sub.A=(V.sub.B+V.sub.C+V.sub.D)/3). As a further example of this
third embodiment, when reference is made to balancing two sets of
cells, where a first set comprises two cells A and B, and the
second set comprises three cells C, D, and E, what is meant is that
the average voltage across cells A and B is being balanced relative
to the average voltage across cells C, D, and E (e.g.,
(V.sub.A+V.sub.B)/2=(V.sub.C+V.sub.D+V.sub.E)/3). The details of
such balancing are discussed later in this disclosure.
[0046] In an embodiment, sets of cells can overlap. For instance,
given three cells, A, B, and C, a first set of cells may comprise
cells A and B. A second set of cells may comprise cells B and C.
Hence, the first and second sets of cells both comprise cell B.
While some embodiments of the energy storage system 100 will
involve balancing the voltages of individual cells relative to
other individual cells, often balancing will take place between
sets of cells.
[0047] For the purposes of this disclosure, a "regulator circuit"
means a circuit configured to minimize a voltage imbalance between
two sets of cells or batteries. In one embodiment, the regulator
circuit 110 may be a modified uk converter as illustrated in FIG.
2. In the illustrated embodiment, the regulator circuit 210 has two
capacitive circuits 222, 224 (optional). The first capacitive
circuit 222 may be connected in parallel with the first battery
202. The second capacitive circuit 224 may be connected in parallel
with the second battery 204. Both of the first and second
capacitive circuits 222, 224 have a first and second terminal. The
first terminal of the first capacitive circuit 222 may be connected
to the first terminal of the first battery 202. The second terminal
of the first capacitive circuit 222 may be connected to the second
terminal of the first battery 202. The first terminal of the second
capacitive circuit 224 may be connected to the first terminal of
the second battery 204. The second terminal of the second
capacitive circuit 224 may be connected to the second terminal of
the second battery 204.
[0048] For the purposes of this disclosure, a "capacitive circuit"
means a combination of interconnected electrical components, or a
single component, capable of storing and discharging charge (or
energy) and/or filtering alternating current (AC) signals. The
energy stored in the capacitive circuits 222, 224 can be used to
mitigate current/voltage spikes by discharging some of the stored
energy. The stored energy can also be used to later supplement
batteries having undesired voltages (either by charging or
supplementing discharge). Similarly, capacitive circuits 222, 224
are also able to dampen or filter certain frequencies of AC signals
such as voltage/current spikes or ripple currents.
[0049] In an embodiment, each capacitive circuit 222, 224 comprises
a single capacitor. In an embodiment, each capacitive circuit 222,
224 comprises multiple capacitors. In an embodiment, each
capacitive circuit 222, 224 comprises multiple capacitors in
parallel. In an embodiment, the capacitive circuits 222, 224
comprise a combination of electrolytic and bipolar capacitors.
Capacitive circuits 222, 224 may include devices that are not
capacitors. For example, other devices such as batteries and gates
of certain transistors have similar properties to capacitors, and
can thus be used in the capacitive circuit 222, 224.
[0050] The regulator circuit 210 also includes an inductive circuit
232, which may be connected to the optional two capacitive circuits
222, 224. The inductive circuit 232 may be connected to the two
batteries 202, 204. The inductive circuit 232 is configured to
store energy (current and/or voltage). The inductive circuit 232
can be charged by energy provided by either battery 202, 204, or
can be charged by bypass energy. Bypass energy is current and/or
voltage that is directed around one of the batteries 202, 204. For
instance, a duty cycle may be applied to the switches 242, 244 such
that during charging energy bypasses the second battery 204 and
instead is stored on the inductive circuit 232. Later, the duty
cycle can be adjusted to allow the energy stored on the inductive
circuit 232 to be distributed to the first battery 202. In another
example, during discharge, energy from the second battery 204 may
bypass the first battery 202 via an adjustment in the duty cycle of
the switches 242, 244. The bypass energy may be stored on the
inductive circuit 232. The duty cycle can be later adjusted, and
the stored energy can be discharged from the inductive circuit 232
and routed to the charger/load 260 or back to the second battery
204.
[0051] For the purposes of this disclosure, an "inductive circuit"
means a combination of interconnected electrical components, or a
single component, capable of resisting changes in current. In an
embodiment, the inductive circuit 232 can comprise one or more
inductors. The inductors may use hollow cores or ferrite cores.
Given high frequency applications, the inductive loops of the
inductors might use litz wire. Since the inductive circuit 232 can
reduce or mitigate ripple currents, the inductive circuit 232 can
be optimized (e.g., size, composition, structure) for known ripple
currents.
[0052] In the illustrated embodiment, a second terminal of the
inductive circuit 232 connects to the following: (1) the second
terminal of the first capacitive circuit 222, (2) the first
terminal of the second capacitive circuit 224, (3) the second
terminal of the first battery 202, and (3) the first terminal of
the second battery 204. In the illustrated embodiment, the
inductive circuit 232 is also connected to two switches 242, 244.
Each of the switches may have a first and second terminal. The
first terminal of the inductive circuit 232 is connected to the
second terminal of the first switch 242 and to the first terminal
of the second switch 244.
[0053] For the purposes of this disclosure, a "switch" means a
device for interrupting and/or diverting current passing through a
conductor. A switch can be either mechanical or electrical. Basic
switches have two states: open (off) or closed (on). However, more
complex switches can have open and closed states as well as states
for diverting current into other conductors. In an embodiment, a
switch is a transistor. There are two major categories of
transistors: field-effect transistors (FET), and bipolar junction
transistors (BJT). Within each of these categories of transistors
are numerous subcategories of transistors. For example, BJT's can
be further specified as NPN, PNP, or heterojunction, and FET's can
be further specified as metal-oxide semiconductor field-effect
transistor (MOSFET) and junction field-effect transistor (JFET).
FET's can further be divided into depletion-mode and
enhancement-mode FET's. It should be understood, that this brief
list of transistors and their subcategories is not exclusive. For
the purposes of this disclosure, a transistor used as a switch may
be in the on state when in saturation mode and in the off state
when in cutoff mode.
[0054] In the illustrated embodiment, the switches 242, 244 are
also connected to the batteries 202, 204 and the capacitive
circuits 222, 224. The first terminal of the first switch 242 is
connected to the first terminal of the first battery 202 and to the
first terminal of the first capacitive circuit 222. The second
terminal of the second switch 244 is connected to the second
terminal of the second battery 204 and to the second terminal of
the second capacitive circuit 224.
[0055] In the illustrated embodiment, the switches 242, 244 are
either open or closed. In an embodiment, the switches 242, 244 are
periodically opened and closed and the first switch 242 is open
when the second switch 244 is closed, and vice versa. The ratio of
time that the first switch 242 is closed relative to the time that
the second switch 244 is closed is called the duty cycle. When both
switches 242, 244 are closed for equivalent periods of time, the
duty cycle is 50%. When the first switch 242 is closed
continuously, and the second switch 244 is open continuously, the
duty cycle is 100%. When the first switch 242 is closed 25% of the
time, and the second switch closed 75% of the time, the duty cycle
is 25%.
[0056] In an embodiment, the controller 250 controls the duty
cycle. In other words, the controller 250 determines for how long
each switch 242, 244 remains closed. In an embodiment, the switches
242, 244 have a third terminal called a gate terminal. The gate
terminal of each switch 242, 244 can be connected to the controller
250. In such an embodiment, the controller 250 controls or drives
the switches 242, 244 via the gate terminal of the switches 242,
244.
[0057] For the purposes of this disclosure, a "controller" means
hardware or software (implemented in hardware) configured to
control the regulator circuit 210. In one embodiment, the
controller 250 is a small single chip micro controller (SCMC). For
example, the controller 250 may be implemented using
Application-Specific Integrated Circuit (ASIC) or
Field-Programmable Gate Array (FPGA). The controller 250 can even
be implemented in discrete, functionally equivalent circuitry, or
in other cases a combination of SCMC and discrete circuitry. In an
embodiment, the controller 250 controls the regulator circuit 210
via pulse width modulation.
[0058] In an embodiment, the controller 250 may be connected to the
first battery 202 and the second battery 204. The controller 250
may monitor the first voltage V.sub.1 across the first battery 202.
The controller 250 may monitor the second voltage across the second
battery 204. From monitoring the voltages V.sub.1, V.sub.2 the
controller 250 can determine if a difference between the first and
second voltage exceeds the voltage imbalance threshold V.sub.T or
identify voltage imbalances between the batteries 202, 204. The
voltage imbalance threshold is a preset number that represents the
allowable margin of voltage difference between two sets of
batteries. For instance, given a first set of batteries operating
at a voltage of 100.2V, a second set of batteries operating at a
voltage of 100.1V, and a voltage imbalance threshold of 0.2V, the
difference between the first and second voltages (0.1V) does not
exceed the voltage imbalance threshold. However, if the first
voltage increases to 100.4V, then the voltage imbalance threshold
is exceeded (i.e., 0.3V>V.sub.T).
[0059] If the voltage imbalance threshold is exceeded, then the
controller 250 can instruct the regulator circuit 210 to balance
the voltages between the first and second batteries 202, 204. In an
embodiment, this involves controlling or driving the switches 242,
244. In an embodiment, this involves adjusting the duty cycle of
the switches 242, 244. In this manner, the controller 250 adjusts
the switch 242, 244 duty cycle such that the voltage imbalances
between the batteries 202, 204 are minimized (the voltages
converge). For example, when the voltages across the two batteries
202, 204 that the regulator circuit 210 is attempting to balance
are equal, the duty cycle can be set to 50%. When a voltage
imbalance exists between the first and second batteries 202, 204,
the controller 250 can adjust the duty cycle of the first switch
242 and the second switch 244 to a value other than 50%.
[0060] The regulator circuit 210 may have inherent losses (e.g.,
impedance of the various components and connections). Thus, greater
efficiency can be achieved by turning the regulator circuit 210 off
when the voltages V.sub.1, V.sub.2 across the batteries 202, 204
are equal or when the difference between voltages V.sub.1, V.sub.2
is less than the voltage imbalance threshold V.sub.T.
[0061] How the controller controls the regulator circuit 210
depends upon whether the batteries 202, 204 are being charged or
discharged. Thus, the controller 210 can monitor the direction of
current flow in the energy storage system 200 and determine whether
the batteries 202, 204 are being charged or discharged.
[0062] While the description of FIGS. 1a and 2 are based on an
energy storage system 100 with two batteries 102, 104, 202, 204 it
should be understood that this description also applies to
configurations where there are more than two batteries and/or more
than one regulator circuit. For instance, the regulator circuit
110, 210 may balance voltages across two sets of batteries, where
each set of batteries has one or more batteries. Examples of such
energy storage systems will be discussed with reference to FIGS. 3
and 4. While the embodiment of the regulator circuits 110, 210
illustrated in FIGS. 1a, 1b, 2 have three terminals, it should be
understood that the regulator circuit 110, 210 may have more or
less than three terminals, and that those terminals may connect to
the sets of batteries/cells at different locations than those
illustrated in FIGS. 1a, 1b, and 2. While the description of FIG.
1b is based on an energy storage system 100 with two cells 102,
104, it should be understood that this description also applies to
configurations where there are more than two cells and/or more than
one regulator circuit.
[0063] FIG. 3 illustrates an embodiment of an energy storage system
having four batteries and two regulator circuits. The energy
storage system 300 includes four batteries 302, 304, 306, 308. The
batteries 302, 304, 306, 308 are connected in series. The energy
storage system 300 is series connected to a charger/load 360. The
energy storage system 300 includes two regulator circuits 312, 314.
In an embodiment, the regulator circuits 312, 314 comprise the
capacitive circuits, the inductive circuit, and the switches
illustrated in FIG. 2. Each regulator circuit 312, 314 may be
configured to balance the voltages across two sets of batteries. In
the illustrated embodiment, the first regulator circuit 312 is
configured to balance a first voltage V.sub.2 across the second
battery 304 and a second voltage V.sub.3 across the third battery
306. In the illustrated embodiment, the first regulator circuit 312
has three connections: (1) to a second terminal of the first
battery 302 and to a first terminal of the second battery 304, (2)
to a second terminal of the second battery 304 and to a first
terminal of the third battery 306, and (3) to a second terminal of
the third battery 306 and to a first terminal of the fourth battery
308.
[0064] In the illustrated embodiment, the second regulator circuit
314 is configured to balance two voltages across two sets of
batteries. One voltage, V.sub.12 comprises the sum of the voltage
V.sub.1 across the first battery 302 and the voltage V.sub.2 across
the second battery 304. Another voltage, V.sub.34 comprises the sum
of the voltage V.sub.3 across the third battery 306 and the voltage
V.sub.4 across the fourth battery 308. The second regulator circuit
314 thus balances the voltages V.sub.12 and V.sub.34 so that
V.sub.12=V.sub.34. The balanced voltages can also be written as
follows: V.sub.1+V.sub.2=V.sub.3+V.sub.4. In the illustrated
embodiment, the second regulator circuit 314 has three connections:
(1) to a first terminal of the first battery 302; (2) to a second
terminal of the second battery 304 and to a first terminal of the
third battery 306; and (3) to a second terminal of the fourth
battery 308.
[0065] Conceptually, balancing the voltages across the batteries
302, 304, 306, 308 occurs as follows. The first regulator circuit
312 balances the voltages across the second battery 304 and the
third battery 306. Since V.sub.2=V.sub.3, when the second regulator
circuit 314 balances the two sets of batteries (302, 304), (306,
308), the voltage across the first battery 302 and the fourth
battery 308 must balance (V.sub.1=V.sub.4).
[0066] The energy storage system 300 may include a controller 350
configured to control the regulator circuits 312, 314. In an
embodiment (not illustrated), the controller 350 may monitor the
voltages across the batteries 302, 304, 306, 308 via connections to
the batteries or to the connections between batteries. In an
embodiment, the controller 350 may monitor voltages via the
regulator circuits 312, 314. If the voltage imbalance threshold
V.sub.T is exceeded, then the controller 350 can instruct the
regulator circuits 312, 314 to balance the voltages across the sets
of batteries that are imbalanced.
[0067] For example, assume that the voltages across the first
battery 302, second battery 304, third battery 306, and fourth
battery 308 are V.sub.1, V.sub.2, V.sub.3, and V.sub.4,
respectively. Assume the energy storage system 300 comprises a 400V
battery where each battery 302, 304, 306, 308 ideally operates at
100V. However, assume that V.sub.1=V.sub.2=V.sub.3=100V, and
V.sub.4=99.8V. Assume the voltage imbalance threshold V.sub.T is
0.1V. The controller 350 does not observe a voltage imbalance
between the two sets of batteries 304, 306 associated with the
first regulator circuit 312 since the difference between V.sub.2
and V.sub.3 is 0V. The controller 350 thus does not change the
instructions provided to, or being provided to, the first regulator
circuit 312 (if the regulator circuit 312 uses switches, then the
duty cycle can be maintained at 50%). On the other hand, the
controller 350 observes a voltage imbalance between the two sets of
batteries (302, 304), (306, 308) associated with the second
regulator circuit 314 since the two voltages across those two sets
of batteries (302, 304), (306, 308) is not equal. The first set of
batteries 302, 304 has a voltage of 200V
(V.sub.1+V.sub.2=100V+100V=200V). The second set of batteries 306,
308 has a voltage of 199.8V (V.sub.3+V.sub.4=100V+99.8V=199.8V).
The difference between these two voltages is 0.2V. Since 0.2V is
greater than the voltage imbalance threshold V.sub.T of 0.1V, the
controller instructs the second regulator circuit 314 to balance
the voltages between the two sets of batteries (302, 304), (306,
308) (if the regulator circuit 312 uses switches, then the duty
cycle is altered from 50%). The controller 350 continues to
instruct the regulator circuit 314 to balance the voltages if the
voltage imbalance falls below the voltage imbalance threshold
V.sub.T. The controller 350 then instructs the regulator circuit
314 to maintain the balanced voltages (if the regulator circuit 312
uses switches, then the duty cycle may return to 50%). The
foregoing values have been used for illustrative purposes only and
in no way are intended to limit the scope of this disclosure.
[0068] Although FIG. 3 only shows a single connection between the
controller and each of the regulator circuits 312, 314, it is to be
understood that such connections represent any number of signal
paths. For instance, in an embodiment where the regulator circuits
312, 314 have two switches each (see for example, FIG. 2), the
controller 350 has two connecting paths to the two switches in each
regulator circuit 312, 314. Alternatively, a single connection can
carry multiple signals, and those signals can be distributed to
multiple switches when the signals reach the regulator circuits
312, 314. For instance, a single connection can carry multiplexed
signals. A demultiplexer can split the two signals from the
multiplexed signal and the split signals could be communicated to
their respective switches. The demultiplexing can take place within
the regulator circuits 312, 314, or external to the regulator
circuits 312, 314.
[0069] In an embodiment (not illustrated), a separate local
controller can be provided for each regulator circuit 312, 314. The
central controller can control these local controllers. Either the
local controllers or the central controller can monitor voltages
across sets of batteries. Additionally, either the local
controllers communicating between themselves or the central
controller can identify voltage imbalances across sets of
batteries. Similarly, either the local controllers communicating
between themselves or the central controller can instruct the
regulator circuits to balance the voltages across sets of batteries
having imbalanced voltages.
[0070] We now move to a discussion of the number of regulator
circuits in an energy storage system. When there are more than two
batteries in an energy storage system, different numbers of
regulator circuits can be used to balance the same number of
batteries. For example, a four-battery energy storage system can be
balanced using two regulator circuits or three regulator circuits.
However, some designs are more efficient than others. In
particular, energy storage systems having 2.sup.n (e.g., 2, 4, 8,
16, 32, 64, etc.) batteries can be very efficient since only
2.sup.n/2 regulator circuits are needed where 2.sup.n is the number
of batteries, and n is any positive integer. While most energy
storage systems having a number of batteries not equal to 2.sup.n
may have more than 2.sup.n/2 regulator circuits, energy storage
systems having 2.sup.n/2 batteries may be designed with as few as
2.sup.n/2 regulator circuits. In other words, energy storage
systems having a number of batteries equal to 2.sup.n can be
implemented with a number of regulator circuits equal to half the
number of batteries.
[0071] FIGS. 3 and 4 illustrate two designs having a number of
batteries equal to 2.sup.n. While the four batteries in FIG. 3 are
balanced by two regulator circuits, in FIG. 4, eight batteries are
balanced by four regulator circuits.
[0072] FIG. 4 illustrates an embodiment of an energy storage system
having eight batteries and four regulator circuits. The energy
storage system 400 includes eight batteries 402, 404, 406, 408,
410, 412, 414, 416. The batteries 402, 404, 406, 408, 410, 412,
414, 416 are connected in series. The energy storage system 400 is
series connected to a charger/load (not illustrated, but note the
two open connections on the left side of the figure which
illustrate where a charger or load can be connected). The energy
storage system 400 includes four regulator circuits 412, 414, 416,
418. In an embodiment, the regulator circuits 412, 414, 416, 418
comprise the capacitive circuits, the inductive circuit, and the
switches illustrated in FIG. 2. Each regulator circuit 412, 414,
416, 418 is configured to balance the voltages across two sets of
batteries as described below.
[0073] In the illustrated embodiment, the first regulator circuit
412 is configured to balance the voltages across the following two
sets of batteries: (1) fourth battery 408; and (2) fifth battery
410. The second regulator circuit 414 is configured to balance the
voltages across the following two sets of batteries: (1) third
battery 406, and fourth battery 408; and (2) fifth battery 410, and
sixth battery 412. The third regulator circuit 416 is configured to
balance the voltages across the following two sets of batteries:
(1) second battery 404, third battery 406, and fourth battery 408;
and (2) fifth battery 410, sixth battery 412, and seventh battery
414. The fourth regulator circuit 418 is configured to balance the
voltages across the following two sets of batteries: (1) first
battery 402, second battery 404, third battery 406, and fourth
battery 408; and (2) fifth battery 410, sixth battery 412, seventh
battery 414, and eighth battery 416.
[0074] The energy storage system 400 may include a controller 450
configured to control the regulator circuits 412, 414, 416, 418.
Although FIG. 4 only shows a single connection between the
controller and each of the regulator circuits 412, 414, 416, 418,
it is to be understood that such connections may represent any
number of signal paths (including multiplexed signals).
[0075] Two examples of 2.sup.n-sized energy storage systems have
been seen. Both balanced the voltages across all sets of batteries
using a number of regulator circuits equal to half the number of
batteries. In comparison, a non-2.sup.n-sized energy storage system
may have more regulator circuits per cell. For example, an energy
storage system having five batteries may be implemented with four
regulator circuits.
[0076] FIG. 5 illustrates an embodiment of an energy storage system
having five batteries and four regulator circuits. The energy
storage system 500 includes five batteries 502, 504, 506, 508, 510.
The batteries 502, 504, 506, 508, 510 are connected in series. The
energy storage system 500 is series connected to a charger/load
(not illustrated, but note the two open connections on the left
side of the figure which illustrate where a charger or load can be
connected). The energy storage system 500 includes four regulator
circuits 512, 514, 516, 518. In an embodiment, the regulator
circuits 512, 514, 516, 518 comprise the capacitive circuits
(optional), the inductive circuit, and the switches illustrated in
FIG. 2. Each regulator circuit 512, 514, 516, 518 is configured to
balance the voltages across two sets of batteries as described
below.
[0077] The first regulator circuit 512 is configured to balance the
voltages across the following two sets of batteries: (1) first
battery 502; and (2) second battery 504, third battery 506, fourth
battery 508, and fifth battery 510. The second regulator circuit
514 is configured to balance the voltages across the following two
sets of batteries: (1) first battery 502, and second battery 504;
and (2) third battery 506, fourth battery 508, and fifth battery
510. The third regulator circuit 516 is configured to balance the
voltages across the following two sets of batteries: (1) first
battery 502, second battery 504, and third battery 506; and (2)
fourth battery 508, and fifth battery 510. The fourth regulator
circuit 518 is configured to balance the voltages across the
following two sets of batteries: (1) first battery 502, second
battery 504, third battery 506, and fourth battery 508; and (2)
fifth battery 510.
[0078] The energy storage system 500 may include a controller 550
configured to control the regulator circuits 512, 514, 516, 518.
Although FIG. 5 only shows a single connection between the
controller and each of the regulator circuits 512, 514, 516, 518,
it is to be understood that such connections may represent any
number of signal paths (including multiplexed signals).
[0079] In an embodiment where switches are used in the regulator
circuits 512, 514, 516, 518 special note must be made regarding the
default duty cycle. In energy storage systems having sets of
batteries consisting of the same number of batteries (see for
example, FIGS. 1-3), the duty cycle when batteries are balanced may
be 50%. However, in embodiments such as illustrated in FIG. 5,
where the numbers of batteries in the sets of batteries are not
equal, the duty cycle when batteries are balanced (the default duty
cycle) may not equal to 50%. For instance, the default duty cycles
for the energy storage system 500 may be as follows: first
regulator circuit 512 has a default duty cycle of 80%; (2) second
regulator circuit 514 has a default duty cycle of 60%; (3) third
regulator circuit 516 has a default duty cycle of 40%; and (4)
fourth regulator circuit 518 has a default duty cycle of 20%. The
non-default duty cycle will differ from these values, as the system
attempts to balance voltage imbalances between sets of batteries.
For instance, the second regulator circuit 514 may be adjusted from
the default duty cycle of 60% to another value (e.g., 59%) when the
batteries that it regulates are not balanced.
[0080] The point of comparing the number of regulator circuits
illustrated in FIGS. 3-5 is not to show that non-2.sup.n-sized
energy storage systems are not useful, but rather simply to show
that 2.sup.n-sizes energy storage systems may be preferred due to
the lower number of regulator circuits per battery in 2.sup.n-sized
systems.
[0081] FIG. 6 illustrates a first embodiment of a method of
operating the herein disclosed energy storage system. The method
600 may include a charging or discharging a battery operation 602.
The battery being charged or discharged can comprise two or more
batteries connected in series.
[0082] While the battery is being charged or discharged, a first
voltage V.sub.1 across a first set of batteries and a second
voltage V.sub.2 across a second set of batteries can be monitored.
As such, the method 600 may include a monitor first voltage V.sub.1
operation 604. The method 600 may also include a monitor second
voltage V.sub.2 operation 606.
[0083] Once the first and second voltages V.sub.1, V.sub.2 have
been monitored (observed or measured), the difference
(|V.sub.1-V.sub.2|) between the first and second voltages V.sub.1,
V.sub.2 can be determined. This difference can be compared to the
voltage imbalance threshold V.sub.T to determine if the voltage
difference exceeds the threshold (|V.sub.1-V.sub.2|>V.sub.T) in
a difference determination 608. If the difference is equal to or
less than the threshold, then the method 600 may loop back to the
monitor operations 604, 606. If the difference is greater than the
threshold, then the controller may instruct the regulator circuit
associated with the voltage imbalance to balance the first voltage
V.sub.1 and the second voltage V.sub.2. The regulator circuit can
balance the first and second voltages by storing bypass energy in
an energy storage unit, and distributing this stored bypass energy
to one of the sets of batteries.
[0084] Simultaneously or sometime thereafter, the method 600 may
loop back to the monitor operations 604, 606.
[0085] FIG. 7 illustrates a second embodiment of a method of
operating the herein disclosed energy storage system. The method
700 is similar to the method 600 with two differences. First, since
the method 700 assumes that the regulator circuits comprise
switches, the method 700 also accounts for duty cycle instructions.
Thus, in the method 700, instructions may be initially provided to
the switches in the one or more regulator circuits to operate at
the default duty cycle (instruct operation 703). For energy storage
systems where the number of batteries in each set of batteries is
equal, the default duty cycle may be 50%. For energy storage
systems where the numbers of batteries in each set of batteries is
not equal, the default duty cycle may be greater or less than 50%.
The exact default duty cycle may depend on the configuration of
regulator circuits.
[0086] Second, if the difference in voltage determination 708
determines that the magnitude of the difference between the
voltages |V.sub.1-V.sub.2| across two sets of batteries is less
than the voltage imbalance threshold V.sub.T, then the method 700
may loop back to the instruct operation 703. In other words, if no
voltage imbalance is monitored, then the method 700 may continue to
instruct the switches to operate at the default duty cycle. If the
voltage imbalance |V.sub.1-V.sub.2| is greater than the voltage
imbalance threshold V.sub.T, then the method 700 may adjust the
duty cycle of the first switch and the second switch in the
regulator circuit via the adjust operation 710. This adjustment
allows energy to bypass one set of batteries, be stored in one or
more energy storage units, and later be distributed to the other
set of batteries. Once the duty cycle has been adjusted, the method
700 may loop back to the monitor operation 704. The monitor
operations 704, 706, the difference determination 708, and the
adjust operation 710 may continue to loop until the difference
between voltages falls below the voltage threshold V.sub.T. At that
point, the duty cycle may return to the default and remain there
until a voltage imbalance greater than the voltage imbalance
threshold is determined.
[0087] It is clear that many modifications and variations of this
embodiment may be made by one skilled in the art without departing
from the spirit of the novel art of this disclosure. These
modifications and variations do not depart from the broader spirit
and scope of the invention, and the examples cited here are to be
regarded in an illustrative rather than a restrictive sense.
[0088] In this regard, any number of the features of the different
embodiments described herein may be combined into single or
multiple embodiments, and alternate embodiments having fewer than,
or more than, all of the features described herein are possible.
Functionality may also be, in whole or in part, distributed among
multiple components, in manners now known or to become known. Thus,
myriad software/hardware/firmware combinations are possible in
achieving the functions, features, interfaces and preferences
described herein. Moreover, the scope of the present disclosure
covers conventionally known manners for carrying out the described
features and functions and interfaces, as well as those variations
and modifications that may be made to the hardware or software or
firmware components described herein as would be understood by
those skilled in the art now and hereafter.
[0089] While various embodiments have been described for purposes
of this disclosure, such embodiments should not be deemed to limit
the teaching of this disclosure to those embodiments. Various
changes and modifications may be made to the elements and
operations described above to obtain a result that remains within
the scope of the systems and processes described in this
disclosure. For example, low-loss capacitors can be used in the
capacitive circuits. Also, the controller may use isolated or
floating connections to the switches of the regulator circuits in
order to prevent damage from voltage/current spikes.
[0090] Numerous other changes may be made that will readily suggest
themselves to those skilled in the art and which are encompassed in
the spirit of the invention disclosed and as defined in the
appended claims.
* * * * *